The invention relates to a gas discharge display device in the form of a plasma panel, comprising a gas filled, gas-tight enclosure in which an insulating matrix member, in the form of an insulating plate, divides the housing into two chambers. The insulating plate is provided with a plurality of apertures therethrough, arranged in an array of rows and columns corresponding in number to the desired number of image points. A plasma electrode is disposed in one chamber which may be in the form of a surface cathode extending parallel with the insulating matrix plate and provided with a luminescent screen electrode which is disposed in the other chamber. A plurality of anode conductors are disposed on the side of the plate facing the cathode electrode and a plurality of control conductors are disposed on the opposite side of the plate facing the screen electrode, with each of the conductors extending around the edges of the associated apertures, and each of the conductors on one side being associated with a respective row of apertures, and each of the conductors on the other side being associated with a respective column of apertures. The cathode electrode is so disposed that, upon application of appropriate potentials to the respective conductors and cathode electrode, a gas discharge can burn in the discharge chamber, and the luminescent screen electrode is disposed sufficiently close to the adjacent conductors on the matrix member that under such conditions a potential of even a few kV applied to such screen electrode cannot trigger any undesired gas discharge. Devices of this type have become known in various embodiments. See, for example, U.S. Pat. Nos. 3,622,829, 3,800,186, 3,845,241 and 3,956,667.
Normally, a gas discharge display contains merely a single chamber in which a plasma is produced, the radiation of which is employed either directly for the optical display or is employed to excite suitable phosphors. Single-chamber arrangements have already proved themselves many times, for example with respect to numerical displays, but their luminosity is not sufficient for the display of fairly large, rapidly changing quantities of information, for example moving pictures. As a result, in spite of considerable efforts, success has not been achieved, as yet, in producing a television picture screen with sufficient brilliance on the basis of such display constructions.
Special gas-discharge panels based on the following principle offer greater luminosity. In such arrangement, the display has two chambers, separated by a suitably perforated control structure. A plasma burns in the chamber at the rear of the structure, as viewed by the observer, while in the front chamber an acceleration anode is disposed a short distance from the control structure, with the distance being sufficiently short that no discharge will occur even with a potential difference of several kV on the anode, in accordance with the so-called Paschen curve. The electrons are drawn out of the discharge chamber through selectively actuated holes or apertures in the control structure, entering the front chamber where they are re-accelerated, impacting a phosphor disposed between the front plate and the acceleration anode. The electrons impact the phosphor with relatively high energy values, thus generating bright dots of light. Relatively high light yields can be obtained with such two-chamber displays, in which the gas discharge serves solely as a source of electrons.
By means of the above described electron generation and re-acceleration principle, utilizing a structure such as illustrated in said U.S. Pat. No. 3,956,667, especially high brightness values can be achieved. According to the concept therein developed, a normal corona burns between a surface electrode running parallel with a matrix member in the form of a control board or plate and the line conductor thereon actually being energized. With this electrode configuration, the cathode emits over virtually its entire area and a plasma is formed in the shape of a prism with the base on the cathode and one edge of the prism on the line being actuated. If the individual apertures in the actuated line are opened by activating the column conductors, disposed at the opposite side of the matrix member, large streams of electrons pass into such apertures, with the velocity spread in the streams of being especially small and the mean energy roughly corresponding to the electron temperature of the plasma.
In all two-chamber models, in particular the highly promising version with a wedge-shaped longitudinal discharge, the formation and technology of the control board or matrix member, with its conductors thereon, and the spacing of the member relative to the other electrodes are of particular importance. The greatest possible number of electrons diffusing towards the apertures in the member should be passed through the actuated apertures from the discharge chamber into the re-acceleration chamber, with the greatest possible bunching and the smallest possible energy scatter. No electrons must pass through the apertures that are not actuated at all or are only half actuated. In order to enable the performance of such control functions, it is not only important that the matrix member and its conductors be correctly designed, but it must also be ensured, above all, that the distance between the acceleration anode and the matrix conductors facing it remain constant over the entire display area. Otherwise the anode would produce locally varying effects on the extremely critical potential conditions in the individual matrix apertures.
It has not proved satisfactory to simply make the conductors carried by the matrix board of elongated, more or less rod-shaped with the conductors on opposed sides of the board crossing over in the centers of the apertures (see FIG. 1 of U.S. Pat. No. 3,622,829). The charged portions of the plasma then charge the edges of the holes in the insulating board whereby the passage of flux becomes impossible. Little improvement is achieved by constructing the column and line conductors of the matrix in strip-like form and provided with apertures having dimensions that are somewhat less than the corresponding diameter of the apertures in the insulating board, i.e. the electrodes mask the insulating member to a certain degree (see FIGS. 2-4 of U.S. Pat. No. 3,622,829), as the side walls of the apertures can still become charged, with unfavorable results. If the size of the apertures is increased, for example, to diameters of about 1 mm, while the charging troubles can be overcome, the influence of the acceleration anode becomes so great that passage of electrons through the apertures can no longer be completely blocked. It has been noted that with relatively large apertures a certain amount of flux constantly enters the re-acceleration chamber, which could not be made to disappear even when a strong negative bias potential, relative to the lines, was applied to the column conductors.